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CB350Cafe first build
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Discussion Starter · #1 ·
Working on some carbs for a friend who has some seized and damaged pilot screws. The bike needs tuning and these have to come out.

Had some angle layin around the shop and made some more progress today on the machining fixture for drilling out the seized pilot screws...the carbs mounted perfectly. I made up some spacers to the tune of .600" to fill in the gap created by the carb nozzles, picked up some 35mm long bolts to secure the carbs to the fixture...they are solid, and I might not even need to use the levelers I added to the base. I will likely need to add a few more slots in the bottom of the fixture so I can secure it and bolt the fixture to the drill press table.



I took off the bracket that holds the two carbs together and used a 6mm transfer punch to locate the holes into the fixture. I plan to use this transfer punch to center punch the damaged pilot screws so the drill bits don't walk or jump around.

I also think I will start with a .250" bit and touch the face of the damages pilot screws, and impart the bit tip profile into the face...maybe I wont need to use the transfer punch...then I will have a perfect lead for subsequent drill bits.

I will start with a 3/32 and move the chain until I get to my tap drill size...a #5 I believe which is .001 below a 5.25mm, and measures .205". The brass and aluminum are soft enough, I think .001 or .0005" will allow some forgiveness.

I am sure there are a few 'steady as she goes' comments coming. I am nervous as failure here is to scrap the carb bodies...don't know what else to do.

Any suggestions?
 
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Littering And...........
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That's actually a quite impressive setup. Very useful if the carb bodies are a rarity in this day and age. As long as you take your time should work well. Personally, I used a reverse thread bolt extractor from a kit my father has. Took the tiniest size they have drilled into the jet, the just put the extractor in and threaded it in until it started finally backing out. We did it in his dining room. He drilled while I held the carbs. I've only had to do this on 2 of the my gsxr carbs bodies and on 2 on my old kz1000.
 

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CB350Cafe first build
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393 Posts
Discussion Starter · #3 ·
....Personally, I used a reverse thread bolt extractor from a kit my father has. Took the tiniest size they have drilled into the jet, the just put the extractor in and threaded it in until it started finally backing out.
thanks for the props...

I am hesitant to try those type extractors because they are such a hard steel, small,...and the heads of these screws are 5/8" deep into the pilot holes. If the extractor breaks off, I am screwed--there is no visual feedback to even see if you are turning the screws--its all blind :mad:

These bodies are pretty rare/pricey if it goes wrong, if I can find them.
 

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Fast ZX-12R
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I've broke off a small e-z out before. What a cluster fuck that was. Go slow and be careful.
 
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CB350Cafe first build
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393 Posts
Discussion Starter · #9 ·
I broke off an intake bolt in my old gs. Then broke off the ez out. Oh Jesus that sucked. Make sure it's centered and level every which way!


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I have levelers built into the fixture :) Hopin' they do their thing.



I AM counting on the fact that I am drilling into brass and aluminum with a pretty robust fixture that will have the centerlines nearly parallel to within thousandths of an inch.

I figured this fixture was the right thing to do if I was going to attempt to drill them out.
 

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CB350Cafe first build
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Discussion Starter · #12 ·
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Administrator
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Thanks Rob! will keep you all posted with pics as I make progress. Hoping for nothing but success :D
I hear ya mate.Most of my stuff here is old School carbs are tha weekest link;)
 

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CB350Cafe first build
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393 Posts
Discussion Starter · #15 ·
Well today was a small victory in that the fixture worked amazingly well for drilling out the pilot screws. So far I was successful in drilling out the first one.

Here is the collage...you can see from the lower left hand corner that the fixture maintained the concentricity fairly well. I was ever so slightly off center, but am very pleased. I have just a simple harbor freight hobby drill press, and I can't believe they can hold a center better than 10 to 15 thousandths.

I was able to fish out both the O-ring as well as the washer. This is the cylinder I was running rich in...interestingly enough, the O-ring came out before the washer did...It may have flipped with some compressed air being shot into the pilot hole...but I doubt it.

I made a hook from a bristle from the bench grinder, and used a hemostat to hold the wire. Worked like a charm.



I will work on the second pilot screw another night. Its a Russian imperial stout (Old Rasputin) for this ol boy in celebration of a successful extraction.

Carb surgery usually never ends well...small victory tonight indeed:dancingmonkey:
 

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CB350Cafe first build
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393 Posts
Discussion Starter · #16 ·
So Old Rasputin is a 9%'r...
I was listening to Mac Lethal, enjoyin my brew...and found it funny that this rap...


while watching the :dancingmonkey: :dancingmonkey: :dancingmonkey:

is rather entertaining...

Oh Ok...I'll have another stout. "cook wit me now uhhh...cook wit me now uhhh, Im makin pancakes...
 

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CB350Cafe first build
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393 Posts
Discussion Starter · #18 ·
Well as it turned out, the second drilling didn't go nearly as perfect as the first, and even though I was only off center by about .010", the threads on the pilot screw are so small, that they didn't hold :(

So plan "B"...

I thought of making a pilot screw for the pilot screw, and thread the main pilot hole (5/16-24). Here is where the carbs are at right now. I will have to seat the real pilot screw to determine the length needed for the back up pilot screw, and then take about 1/32" off of the radius for about one inch up the threaded portion, then cut the head off and slot the threaded end.



This is about the only other option I could come up with.
 

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CB350Cafe first build
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393 Posts
Discussion Starter · #19 ·
So since I don't have a lathe, I thought up this idea at lunch...using the air cutoff wheel in tandem with the drill press. I fixed the cutoff and can rotate the cutoff disc in and stroke the press into the wheel.



I need to figure out the lengths now, trim the straight portion, and then grind a shoulder, face and cut a screw driver slot into the threaded end.

This only took about 15 minutes to grind down the head, threads and face the one end.
 

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I bang metal
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So since I don't have a lathe, I thought up this idea at lunch...using the air cutoff wheel in tandem with the drill press. I fixed the cutoff and can rotate the cutoff disc in and stroke the press into the wheel.



I need to figure out the lengths now, trim the straight portion, and then grind a shoulder, face and cut a screw driver slot into the threaded end.

This only took about 15 minutes to grind down the head, threads and face the one end.
wow, that is impressive! I am impressed now but if i was standing around while it was being used i would probably be scared as hell haha. Glad it worked out for you!
 
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